According to the state of the art, wood-derived panels, such as chip-boards, fiber boards, plywood panels, wood core plywood, panels from cellulose waste or laminates from a plurality of layers of resin-laminated core papers are coated on a large scale with decoratively printed or dyed support sheets, which generally are impregnated with aminoplast resins curable at elevated temperatures and coated with curable or thermoplastic condensation or polymerization resins. Products with particularly advantageous use properties are obtained if melamine-formaldehyde precondensates are used for the impregnation while curable polymerization resins, such as copolymers, which are based on (meth)acrylate esters, or unsaturated polyester resins are employed for the coating. This state of the art is described in greater detail, for example, in DE-C No. 2,734,669 and DE-C No. 3,403,691.
Such support sheets, intended for finishing or improving surfaces, are generally prepared by first impregnating the paper sheets, which are to be used as support sheets, with the aqueous solution of a curable aminoplast resin precondensate. In so doing, the cellulose fibers of the support sheet should be enveloped completely. This generally requires an amount of aminoplast resin (calculated as solid resin) of 50 to 100% of the weight of the paper. The sheets so obtained are dried so as to avoid the complete curing of the aminoplast resin. The impregnated support sheets can be coated by dissolving the coating resin in a suitable solvent, such as methylene chloride, methyl ethyl ketone, tetrahydrofuran or solvent mixtures and pouring the solution obtained on the impregnated support sheet. The solvent is then evaporated off.
To achieve a decorative surface, the support sheet used to finish the surface is printed with a decor to match the application or dyed a uniform color. The transparent coating lacquers should allow the decor or the uniform color to shine through brilliantly and clearly.
The surface of the sheet-like support, such as a chipboard, can be improved with the synthetic resin-containing support sheet by pressing the decorative, resin-impregnated support sheet onto the support in a hot press at temperatures of about 130.degree. to 180.degree. C. and a pressure of about 0.3 to 10 N/mm.sup.2, using platens. In so doing, the resin cover layer assumes a degree of gloss, which corresponds to that of the surface of the platen. It is also possible to cure the resin-impregnated support sheets by themselves and to then glue them onto the support sheets, using glue presses if necessary. In the case of laminates which consist of several layers of curable resin-impregnated core paper, the formation of the laminate by pressing the resin-impregnated core paper while curing the impregnating resins and the surface improvement can be carried out simultaneously in one step.
The surfaces of asbestos cement boards or gypsum plaster boards can be improved in much the same way as those of wood-derived panels. The surfaces of sheet-like components, such as panels with a honeycomb structure, which are produced in lightweight construction processes and optionally coated with metal foil, such as aluminum foil, can also be improved.
Sheet-like materials, the surface of which is improved in such a manner, combine good use properties of the surfaces (abrasion resistance, scratch resistance solvent resistance) with a decorative, aesthetically pleasing effect. The surface-improved, sheet-like materials are therefore preferred for the manufacture of objects with decorative surfaces such as doors, furniture, table tops, facade elements, exhibition booths, or for the decoration of rooms, such as foyers, waiting rooms, switch rooms, etc.
The surfaces may also be structured or patterned. Structuring is accomplished during the pressing while using a compression mold or tool with a relief-type surface, the structure or pattern of which is reproduced in negative form on the surface improving layer. With pronounced, deep profiling and the use of differently dyed synthetic resin layers, special color effects can be achieved because the first layer of synthetic resin, facing the compression tool during the pressing, is pushed away from the raised areas of the compression mold and flows away to the areas of lesser pressure. Corresponding to the raised areas of the profile of the compression tool, the color of the second resin layer and/or the color of the dyed or printed support sheet can be recognized. Such a method is disclosed in the German Auslegeschrift No. 2,650,560.